Laser digitizer system for dental applications

ABSTRACT

An intra-oral laser digitizer system provides a three-dimensional visual image of a real-world object such as a dental item through a laser digitization. The laser digitizer captures an image of the object by scanning multiple portions of the object in an exposure period. The intra-oral digitizer may be inserted into an oral cavity (in vivo) to capture an image of a dental item such as a tooth, multiple teeth or dentition. The captured image is processed to generate the three-dimension visual image.

PRIORITY AND CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of Ser. No. 10/804,694, filed Mar.19, 2004.

BACKGROUND OF THE INVENTION

1. Related Field

The invention relates to three-dimensional imaging of physical objects.In particular, the invention relates to intra-oral (in vivo) laserimaging of dental items including dentition, prepared dentition,impression materials and the like.

2. Description of the Related Art

A three-dimensional (“3D”) visual image of a physical object may begenerated by a computer that processes data representing shapes,surfaces, contours and/or characteristics of the object. The data isgenerated by optically scanning the object and detecting or capturingthe light reflected from the object. Principles such as Moir,interferometry, and laser triangulation, may be used to model the shape,surfaces, contours and/or characteristics of the object. The computerdisplays the 3D image on a screen, or computer monitor.

Existing intra-oral 3D imaging systems use a variation of the Moireimaging technique. Such systems use structured white light to project atwo-dimensional (“2D”) depiction on the object to be imaged. Moirsystems use the 2D lateral information, and input from skilledoperators, to determine relative dimensions of adjacent features. Moiresystems also use a sinusoidal intensity pattern that is observed from aposition other than a projection angle that does not appear sinusoidal.Therefore, an inferred point-by-point phase angle between an observedand a projected image may be correlated to height data.

Intra-oral dental imaging systems, based on the Moiré technique image adental item, such as a tooth, directly from or below occlusal surfacesof the tooth. Such systems have low depth resolution and may notaccurately image or represent a surface that is undercut or shadowed.Intra-oral dental imaging systems also may require a powder or the liketo provide a uniform color and reflectivity required by limitations ofthe white light techniques. The powder layer may increase or introduceerrors in the digitized data, due to non-uniformity of the powderthickness.

BRIEF SUMMARY OF THE INVENTION

The embodiments provide a laser imaging system that generates athree-dimensional image of a scanned physical object such as a dentalitem. An embodiment includes intra-oral laser imaging systems, methods,apparatuses, and techniques that provide digitization of a physicalobject to generate a 3D visual image of the object. An intra-oraldigitizer generates a laser pattern that may be projected on or towardsa dental item, dentition, prepared dentition, or impression material inan oral cavity (in vivo). The intra-oral digitizer may include aprojection optics system that remotely generates the laser pattern andrelays that pattern so that it may be projected on or towards a dentalitem or items in vivo. The intra-oral digitizer also includes an imagingoptical system that detects or captures light reflected from the dentalitem. The imaging optical system, or a portion thereof, may be insertedin the oral cavity at a known angle with respect to the projectionsystem to capture light reflected from the dentition. The captured lightmay be used to generate data representative of the 3D image of thedentition. The 3D visual image may be displayed on a computer monitor,screen, display, or the like. The data also may be used to form a dentalrestoration using known techniques such as milling techniques. Therestoration may be a crown, bridge, inlay, onlay, implant or the like.

The intra-oral laser digitizer may have a light source, a focusingobjective, a two-axis scanner, an optical relay system, an image opticssystem, and a processor configured to carry out instructions based oncode, and process digital data. The light source may have a laser LEDand collimating optics producing a collimated beam of light that isprojected to the two-axis scanner. The scanner redirects, or scans, thecollimated beam of light through at least two axes at high speeds. Thescanner may scan the beam at a selected constant frequency or a variablefrequency and duty cycle. The scanned beam is projected toward theoptical relay system, which focuses the beam as a dot on the surface ofthe object.

The optical relay system may include focusing lenses, relay lenses and aprism, through which the scanned beam may be projected. The opticalrelay system focuses the desired pattern of the laser dot generated bythe scanner on the object. The laser dot may be focused so that the dottraverses a curvilinear segment across the object. The optical relaysystem may include one or more optical components such as standardoptical glass lenses, or gradient index glass lenses.

The image capture instrument detects the light reflected from the objectthrough a relay optics system. The image capture system generates datarepresenting a captured image of the scanned beam. The image capturesystem may be configured to capture images of one or more scannedcurvilinear segments during an exposure period. The computer processesthe data to generate the three-dimensional visual image of the object ona computer monitor, a screen, or other display.

Multiple images of the object may be recorded and processed by thecomputer to produce a 3D map of the object. The multiple images can becaptured from multiple positions and orientations with respect to theobject. The individual images are merged to create an overall 3D map ofthe object. The images may be captured and processed to provide a realtime image of the surface of the object. The real time image may providean instant feedback mechanism to an operator of the system. Thedigitizer system may include software that displays the overall 3D imagecaptured in real time. The software also may include feedback andidentification provided to the operator of suggested viewpoints tocomplete the overall 3D image. The software also may identify crucialfeatures in the scanned data set during a data acquisition process.These features include margins and neighboring dentition. This softwarealso may display highlighted features or possible problem areas, as theoperator captures additional viewpoints.

A one- or two-axis tilt sensor may determine a relative angle betweenimages. The imaging system may also be used as a standard 2D dentalcamera through the addition of a background light source.

Control, acquisition, and interaction may be initiated via footcontrols, controls on the intra-oral device, or by voice recognition ofspoken commands, or like methods.

An embodiment quickly and accurately digitizes 3D surfaces of an object,such as prepared teeth and impression materials including biteregistration strips. The intra-oral digitizer also provides improvedimaging abilities over prior art intra-oral dental imaging systems. Thedigitizer also simplifies operator requirements and interactions for anintra-oral dental scanning system.

Other systems, methods, features and advantages of the invention willbe, or will become, apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereferenced numerals designate corresponding parts throughout thedifferent views.

FIG. 1 illustrates an intra-oral laser digitizer coupled to a processor.

FIG. 2 illustrates a front view of a portion of the intra-oral laserdigitizer of FIG. 1.

FIG. 3 illustrates a top view of the intra-oral laser digitizer of FIG.1.

FIG. 4 illustrates a side view the intra-oral laser digitizer of FIG. 1.

FIG. 5 illustrates an imaging optical system of the intra-oral laserdigitizer of FIG. 1.

FIG. 6 illustrates a projection optics system of the intra-oral laserdigitizer of FIG. 1.

FIG. 7 illustrates a projection of a laser light beam on an object.

FIG. 8 illustrates a top view of a projection of a laser light beam.

FIG. 9 illustrates a two-axis scanner of the intra-oral laser digitizerof FIG. 1.

FIG. 10 illustrates an image of a light pattern of the intra-oraldigitizer, as projected on and viewed from a flat surface.

FIG. 11 illustrates the light pattern of FIG. 10 as projected on anobject to be imaged.

FIG. 12 illustrates a reflection of the light pattern of FIG. 10 asdetected by image capture instrument.

FIG. 13 illustrates multiple laser profiles projected towards an object.

FIG. 14 illustrates an electronic circuit that for controlling thegeneration of a line pattern.

FIG. 15 illustrates an intra-oral digitizer with a low coherence lightsource coupled to the scanning system and a coupler to a reference beamon an optical delay line.

DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates an example of an intra-oral laser digitizer 100.FIGS. 2-5 illustrate various views of the intra-oral laser digitizer 100of FIG. 1. The intra-oral digitizer 100 generates a 3D image of anobject 108 such as a dental item. The intra-oral digitizer 100 generatesa laser pattern that may be projected on or towards a dental item,dentition, or prepared dentition in an oral cavity (in vivo). Theintra-oral digitizer 100 may remotely generate the laser pattern andrelay the pattern towards the dental item or items in vivo. The laserpattern may be relayed through relay optics such as prisms, lenses,relay rods, fiber optic cable, fiber optic bundles, or the like. Theintra-oral digitizer 100 also may detect or capture light reflected fromthe dental item in vivo. The intra-oral digitizer 100, or a portionthereof, may be inserted in the oral cavity to project the laser patternand to detect the reflected laser pattern from the dental item or itemsin the oral cavity. The captured light may be used to generate datarepresentative of the 3D image of the dentition. The data may be used todisplay the 3D image. The data also may be used to form a model of theobject using known techniques such as milling techniques. The model ofthe object may be a dental restoration such as a crown, bridge, inlay,onlay, implant or the like. The data also may be used for diagnosticpurposes.

The laser digitizer 100 includes a laser light source 101, a firstscanner 102 (x scanner), a second scanner 103 (y scanner), a lensassembly 104, a first reflecting prism 113, a first optics relay 105, asecond reflecting prism 107, a third reflecting prism 106, a secondoptics relay 109, imaging optics assembly 110, imaging sensor 111, andan electronic circuit 112. The intra-oral laser digitizer 100 may becoupled to a processor 119.

The laser light source 101 may include collimating optics (not shown)that generate a laser beam of light 122 from the light source 101. Thecollimated light beam 122 is characterized by parallel rays of laserlight. The laser beam 122 is projected to the first scanner 102.

The laser light source 101 may include a laser diode or LED thatgenerates a laser light beam having an elliptical-shaped cross-section.The collimating optics may be configured to circularize the ellipticalbeam and to generate a circular spot. The circular spot may be used toscan a uniform line across the surface of the object 108. The laserdiode may be any commercially available laser diode configured to emit alaser light beam, such as the Blue Sky Research Mini-Laser 30 mWattlaser with 0.6 mm collimated beam, model number Mini-635D3D01-0.

The laser light source 101 also may modulate the laser light beam. Thelaser light source 101 may be coupled to a modulator that adjusts orinterrupts light flow from the source at high modulation or switchingrate. The modulation may be in the range of substantially 1 kHz tosubstantially 20 MHz. A scan pattern may be generated on the object, bymodulating the laser light source 101.

The first scanner 102 includes an x-scanner mirror having asubstantially flat reflecting surface. The reflecting surface of thex-scanner mirror, may be rectangular-shaped having dimensionsapproximately 1.5 mm by approximately 0.75 mm. The laser beam 122 fromthe light source 101 may have a width no greater than the smallestdimension of the first scanner 102. For example, the width of the laserbeam may be approximately 0.6 mm. The beam of light 122 from the laserlight source 101 is incident upon the reflecting surface of the firstscanner 102.

The second scanner 103 includes a y-scanner mirror having asubstantially flat reflecting surface. The reflecting surface of they-scanner mirror, may be rectangular-shaped having dimensionsapproximately 1.5 mm by approximately 0.75 mm. The reflecting surfacesof the x-scanner and the y-scanner may be mirrors or the like.

FIG. 2 illustrates the second scanner 103 positioned substantiallyorthogonal to the first scanner 102. The first scanner 102 directs thebeam of light 122 towards the second scanner 103. The beam 122 directedfrom the first scanner 102 is incident upon the reflecting surface ofthe second scanner 103. The first scanner 102 directs the beam 122 alongan arc onto the reflecting surface of the second scanner 103. Thereflective surface of the first scanner 102 may be rotated through anaxis of rotation to create the arc on the reflective surface of thesecond scanner 103. Together, the reflecting surfaces of the firstscanner 102 and the second scanner 103 form a two-axis scanner assembly116. The reflective surface of the second scanner 103 rotates throughthe y-axis to direct a two-axis scanned beam 124 in an orthogonaldirection.

The scanned beam 124 is incident upon the lens assembly 104. The lensassembly 104 focuses the scanned beam 124 through the first reflectingprism 113. The first reflecting prism 113 directs a scanned image 125 tothe first optics relay 105.

FIG. 3 illustrates the first optics relay 105 relaying the scanned image125 to the second reflecting prism 107. The second reflecting prism 107may be inserted into an oral cavity to project the laser pattern towardone or more dental items to be imaged. The first optics relay 105transmits the laser pattern generated by the light source 101, the firstand second scanner 102, 103 and the lens assembly 104 to a remotelocation, such as an oral cavity. The second reflecting prism 107projects a scanned beam 114 towards the object 108 so that a lightpattern may be projected on the object 108. The first optics relay 105may be any commercially available relay optics system. The first opticsrelay 105 may be a relay lens such as a GRIN lens, a fiber optic cable,a fiber optic bundle, or similar device for relaying an optical imageover a distance L1. An example of a first optics relay 105 is a GrinTechrod lens with part number 125340824C-9 attached to the GrinTechobjective grin lens with part number CR1032-2.

As shown in FIG. 4, a reflection 115 of the scanned beam 114 from thesurface of the object 108 is captured through the third reflecting prism106 to relay captured reflection 126. The third reflecting prism 106 maybe inserted into an oral cavity to detect or capture reflections of thelaser pattern from the one or more dental items to be imaged. The secondoptics relay 109 transmits captured reflection 126 for a distance L2from the oral cavity to the imaging optics assembly 110. The capturedreflection 126 from the object 108 is imaged and focused by the imagingoptics 110 to provide a focused beam 127. The focused beam 127 isprojected towards the imaging sensor 111. The imaging sensor 111 may bea CCD sensor, a CMOS sensor, or other light sensitive device or array oflight sensitive devices. The second optics relay 109 may be anycommercially available relay optics system. The second optics relay 109may be a relay lens such as a GRIN lens, a fiber optic cable, a fiberoptic bundle, or similar device for relaying an optical image over adistance L2. An example of the second optics relay 109 is the GrinTechrod lens with part number 12534082-4C attached to the GrinTech objectivegrin lens with part number CR1032-2.

The imaging sensor 111 may be coupled with electrical circuit 112. Theelectrical circuit 112 may include electrical and electronic componentssuitable for processing electrical signals of the intra-oral digitizer100. The electrical circuit 112 may be located or enclosed within asuitable enclosure. The enclosure may be a hand-held enclosure or have aform factor suitable for being handheld, for enclosing the electricalcircuit 112 and for manipulating the intra-oral digitizer 100 in vivo.The enclosure and electrical circuit may be remotely located from thesecond and third reflecting prisms 107, 106. The electrical circuit 112may modulate the light source 101, and drive the scanning mirrors 102and 103. The electrical circuit also may gather electronic data receivedfrom the imaging sensor 111. The electrical circuit also may performadditional processing and communication with an external processor 119via a cable or wireless or some other communications link.

FIG. 5 illustrates an imaging optics system 120 of the laser digitizer100. The imaging optics system 120 may include the third reflectingprism 106, the second optics relay 109, the imaging optics 110 and theimaging sensor 11. The imaging optics system 120 generates a digitalsignal representative of the capturer reflection 126.

FIG. 6 illustrates the projection optics system 121, including the lensassembly 104, the first reflecting prism 113, the first optics relay105, and the second reflecting prism 107. The projection optics system121 may project the scanned image in the direction of the object 108 soas to project the laser pattern in vivo.

FIG. 7 illustrates a front view of a portion of the intra-oral laserdigitizer 100. The scanned beam 114 is directed from the projectionoptics system 121 in the direction of the object 108. Reflected light115 is captured or detected by the imaging optics system 120. Theimaging optics system 120 may be characterized by a coordinate systemhaving axes X, Y, Z and the projection optics system 121 may becharacterized by a coordinate system having axes X′Y′Z′. The Z′ axisprojects vertically from a center of the second reflecting prism 107 tothe object 108, and Z is the axis projected vertically from the surfaceof the object at 108 to a center of the third reflecting prism 108. TheX′ axis is orthogonal to the Z′ axis and in a horizontal plane withrespect to the front of the intra-oral device 100. The X axis isorthogonal to the Z axis. The Y′ axis may be defined according to the X′axis and the Z′ axis in a right-handed coordinate system, as illustratedin the top view of the second reflecting prism 106 and the thirdreflecting prism 107, as illustrated in FIG. 8. The Y axis may bedefined according to the X′ axis and the Z′ axis in a right-handedcoordinate system, as illustrated in the top view of the secondreflecting prism 106 and the third reflecting prism 107, as illustratedin FIG. 8.

An angle between the Z axis and Z′ axis may be designated as θ. Adistance from a center of the third reflecting prism 106 to the point onthe object 108 may be referred to as d1 and a distance from the centerof the third reflecting prism 106 to a top of a depth of focus regionmay be referred to as d2.

FIG. 9 illustrates a two-axis scanner assembly 116. The two-axis scannerassembly may include the first scanner 102 and the second scanner 103.The first scanner 102 includes a reflective surface that rotates aboutaxis 117. The reflective surface of the first scanner 102 directs thelight to the reflecting surface of the second scanner 103. Thereflective surface of the second scanner 103 rotates about the axis 118.

The reflective surfaces of the scanners 102 and 103 may be rotatablycoupled with a respective motor, other electromagnetic drivingmechanism, or electrostatic driving mechanism such as magnets, coils orother electromagnetic coupling that control a rotational movement of thecorresponding reflective surface to effect the scanning of thecollimated light beam.

The two-axis scanner 116 redirects, or scans, the collimated light beamto form a scanned light beam 114 having a position that varies overtime. The scanned beam 114 is directed by the two-axis scanner 116 tothe lens assembly 104 and the first optics relay 105. The two-axisscanner 116 redirects the collimated light beam in at least two or moreaxes 117, 118 where each axis is substantially perpendicular to the axisof the collimated light beam. The first and second scanners 102, 103 mayhave essentially perpendicular axes, and may be essentially orthogonalwith respect to each other. The scanners 102, 103 also may be positionedat an arbitrary angle relative to each other.

Additional scanners also may be included to scan the collimated lightbeam. The scanners 102, 103 may be positioned orthogonally so that thecollimated laser beam incident on the reflectors may be scanned orredirected in at least two axes. The first scanner 102 scans the beamalong one axis, such as an x-axis. The second scanner 103 may bepositioned so that the beam along the x-axis incident upon the secondscanner 103 may be scanned along an orthogonal direction to the x-axis,such as a y-axis. For example, the first and second scanner 102, 103 maybe positioned orthogonal with respect to each other so that the firstscanner 102 scans the beam along the x-axis and the second scanner 103scans the beam along an orthogonal direction to the x-axis, such as ay-axis.

The first scanner 102 also may have a spinning polygon mirror such thatthe rotatable second reflector 103 and the spinning polygon reflector102 together also are configured to scan the laser beam in two axes. Thespinning polygon mirror 102 may scan the collimated light beam along anx-axis and the rotatable mirror 103 may scan the collimated light beamalong a y-axis. Each axis, the x-axis and y-axis, may be substantiallyorthogonal with one another to generate a scanned light beam along twosubstantially orthogonal axes.

The two-axis scanner 116 also may include a single reflecting surfacethat scans a beam of light along two axes. The reflecting surface may bedriven electromagnetically or electrostatically to rotate the reflectingsurface about two essentially orthogonal axes individually orsimultaneously.

The two-axis scanner 116 may be include one or moreMicroelectro-mechanical systems (“MEMS”), which have reflecting surfacesthat may be driven electromagnetically or electrostatically or using apiezo crystal or otherwise mechanically to rotate the reflecting surfaceabout two essentially orthogonal axes individually or simultaneously.

The two-axis scanner 116 also may include a programmable positioncontroller. The position controller may be a component of the two-axisscanner 116 or may be incorporated with the electronic circuit 112. Thecontroller may control movement of the scanners 102, 103 by providingcontrol signals to the drive mechanisms of the reflective surfaces ofthe scanners 102, 103. The controller controls the movement of thescanners 102, 103 so that the collimated laser beam is redirected toprovide to a scan sequence. The coordinate system for the two-axisscanner 116 is referred to as X′Y′Z′.

As shown in FIGS. 7 and 8, the object 108 to be imaged is positionedwithin a field of view of projection optics 121 and the imaging opticssystem 120. The projection optics 121 is positioned at the angle θ withrespect to an optical axis of the imaging optics system 120 so that whenthe focused dot is scanned across the surface of the object 108 thelight is reflected towards the imaging optics system 120 at angle θ. Thetwo-axis scanner 116 moves the scanned beam 114 so that the focus pointof the laser dot from the projection optics 121 traverses through apattern across the surface of the object 108.

The imaging optics system 120 may be configured and/or positioned tohave a field of view that includes the focused laser dot projected onthe object 108. The imaging optics system 120 detects the laser dot asit is scanned across the surface of the object 108. The imaging opticssystem 120 includes an image sensor 111 that is sensitive to the lightreflected from the object 108. The imaging optics system 120 may includean imaging lens 110 and an image sensor 111 and the second optics relay109 and a prism or fold mirror 106. The imaging lens 110 is configuredto focus the light reflected from the object 108 towards the imagesensor 111. Based on a light detected from the object 108, the imagesensor 111 generates an electrical signal representative of the surfacecharacteristics (e.g., the contours, shape, arrangement, composition,etc.) of the object 108.

The image sensor 111 captures an image of the scanned surface of theobject 108. The image sensor 111 may be a photo-sensitive or lightsensitive device or electronic circuit capable of generating signalrepresentative of intensity of a light detected. The image sensor 111may include an array of photodetectors. The array of photodetectors maybe a charge coupled device (“CCD”) or a CMOS imaging device, or otherarray of light sensitive sensors capable of generating an electronicsignal representative of a detected intensity of the light. The imagesensor 111 may comprise a commercially available CCD or CMOS highresolution video camera having imaging optics, with exposure, gain andshutter control, such as the Silicon Imaging USB Camera SI-1280F-U.

Each photo-detector of the image sensor 111 generates an electric signalbased on an intensity of the light incident or detected by thephoto-detector. In particular, when light is incident to thephoto-detector, the photo-detector generates an electrical signalcorresponding to the intensity of the light. The array ofphoto-detectors includes multiple photo-detectors arranged so that eachphoto-detector represents a picture element, or pixel of a capturedimage. Each pixel may have a discrete position within the array. Theimage capture instrument 120 may have a local coordinate system, XY suchthat each pixel of the scanned pattern corresponds to a uniquecoordinate (x,y). The array may be arranged according to columns androws of pixels or any other known arrangement. By virtue of position ofthe pixel in the array, a position in the image plane may be determined.The imaging optics system 120 converts the intensity sensed by eachpixel in the image plane into electric signals that represent the imageintensity and distribution in an image plane.

The CMOS image sensor may be configured to have an array of lightsensitive pixels. Each pixel minimizes any blooming effect such that asignal received by a pixel does not bleed into adjacent pixels when theintensity of the light is too high.

The two-axis scanner 116 may be configured to scan the laser beam 114across the surface of the object 108 via the projection optics 121 invarious patterns. The pattern may cover a portion of the surface of theobject 108 during a single exposure period. The pattern also may includeone or more curves or any known pattern from which the characteristics,elevations and configurations of the surface of the object 108 may beobtained.

During an exposure period, an image of a portion of the surface of theobject is captured. The beam 114 scans the object 108 via the two-axisscanner 116 and the projection optics 121 in a selected pattern,allowing the imaging sensor 111 to detect the light reflected fromobject 108. The image sensor 111 generates data representative of thesurface characteristics, contours, elevations and configurations of thescanned portion or captured image. The data representation may be storedin an internal or external device such as a memory.

FIG. 10 illustrates an example of a scanned pattern of light 1048 asviewed from a substantially flat surface. The scanned pattern 1048 mayinclude multiple curves 1050-1055 that are generated by the scanner 116.A portion of the curves 1050-1051 may be essentially parallel to eachother. The curves 1050-1055 also may represent or include a connectedseries of points or curvilinear segments where a tangent vector n at anysingle point or segment obeys the following rule:|n·R|≠0  (1)where R is a triangulation axis that is substantially parallel to Y andY′ and passes through an intersection of an axial ray from the thirdreflecting prism 106 of the image optics system 120 and an axial rayfrom the second reflecting prism 107 of the optical projection system121. Accordingly, the angle between the tangent n at any point orsegment of the curve and the triangulation axis R is not 90 degrees.Each curve 1050-1055 also may have a cross-sectional intensitycharacterized by a function that may have a sinusoidal variation, aGaussian profile, or any other known function for cross-sectionalintensity. In an embodiment, a minimum angle between a valid ray betweenthe second reflecting prism 107 relative to a valid axial ray of thethird reflecting prism 106 is non-zero.

During a subsequent scan period, the beam 114 is scanned in a patternacross an adjacent portion of the object 108 and an image of theadjacent portion is captured. The scanned beam 114 may scan a differentarea of the surface of the object 108 during subsequent exposureperiods. After several exposure periods in which the beam 114 is scannedacross the various portions of the object 108 and images of thosescanned portions captured, a substantial portion of the object may becaptured.

The processor 119 may be coupled to the imaging optics system 120 andconfigured to receive the signals generated by the image captureinstrument 120 that represent images of the scanned pattern on theobject 108. The processor 119 may process and display the signalsgenerated by the image optics system 120. The processor 119 also may becoupled to the laser light source and control selected or programmedapplications of the laser light. The processor 119 also may be coupledwith the two-axis scanner 116 and programmed to control the scanning ofthe collimated light

The image optics system 120 may be characterized by a local coordinatesystem X, Y, Z, where the X and Y coordinates may be defined by theimage imaging optics system 120. A value for the Z coordinate may bebased on the distance d₁ and d₂ so that d₁≦z≦d₁. A point from aprojected curve incident to a plane perpendicular to Z will appear to bedisplaced in the X direction by Δx. Based on a triangulation angle, thefollowing condition may exist: $\begin{matrix}{{\Delta\quad z} = \frac{\Delta\quad x}{{Tan}\quad\theta}} & (2)\end{matrix}$

For a given curve (e.g. curve 1050) in the projection pattern there maybe unique relations θ(y), z_(base)(y) and x_(base)(y). The relationsθ(y), z_(base)(y) and x_(base)(y) relations may be determined throughcalibration. The calibration may be performed for example by observingthe curve 1050 as projected on a plane surface. The plane surface may beperpendicular to the imaging optics system 120 at two or more distancesd along the Z axis from the image optics system 120. For each y valuealong the curve 1050, using at least two such curves with known z valuesof z₁ and z₂, where z₁<z₂, Δz may be computed as Δz=z₂−z₁. A value Δxmay be observed using imaging optics system 120. Using equation (2),θ(y) may be computed. The corresponding value z_(base)(y) may be setequal to z₁. The corresponding value x_(base)(y) may be equal to an xvalue at the point y on the curve corresponding to z₁. Additional curvesmay be used to improve accuracy of through averaging or interpolation.

FIG. 11 illustrates the scanned pattern of light 1148 projected on theobject 1180 to be imaged. FIG. 12 illustrates the light patternreflected from the object 1180 as incident to the image sensor 1234. Forthe observed projected curves 1250-1255 on the object, each curvecorresponds to one of the curves 1150-1155 shown in FIG. 11 and acorresponding one of the curves 1050-1055 shown FIG. 10. Accordingly,for each curve 1250-1255, the corresponding relations θ(y), z_(base)(y)and x_(base)(y) may be selected that were pre-computed during acalibration. For each point (x_(observed), y_(observed)) on each curve1250-1255,Δx=x _(observed) −x _(base)(y _(observed))  (3)Equation (2) may be used to determine Δz using θ(y_(observed)), andconsequentlyz _(observed) =Δz+z _(base)(y _(observed))  (4)The collection of points (x_(observed),y_(observed),z_(observed))obtained, form a 3D image of the object 1180.

A maximum displacement for a curve may be determined by:Δx=(d ₁ −d ₂)Tan θ  (4)A maximum number n_(max) of simultaneously distinguishable curves 1050may be determined according to n_(max)=X_(max)/Δx or equivalently$\begin{matrix}{n_{\max} = \frac{X_{\max}}{\left( {d_{1} - d_{2}} \right){Tan}\quad\theta_{\max}}} & (5)\end{matrix}$The number n_(max) increases with a decreasing depth of field d₁−d₂ andincreases with a smaller θ_(max). The accuracy of the determination alsomay decrease with smaller θ_(max) values.

Where the number of curves n exceeds n_(max), any ambiguity in thelabeling of the lines may be resolved by associating the observed curvesinto groups of adjacent curves. For each group of adjacent curves, if atleast one curve is correctly labeled, then all other curves in thatgroup may be labeled using adjacency. A method to determine the correctlabeling of at least one curve in a group may include considering asecond pattern where the number of curves is less than n_(max) and maybe at an angle relative to the first pattern. The curves of the secondpattern may be properly labeled, and intersections of the curves of thesecond pattern with the curves of the first pattern may be used todeduce labeling of some subset of the curves in the first pattern. Thismay be repeated with additional patterns until all curves are correctlylabeled.

FIG. 13 illustrates scanned lines 1350-1352 on the surface of an object.The scanned line 1350 has associated with it a region bounded by theboundary curves 1360 and 1362. The region bounded by boundary lines 1360and 1362 is determined by a pre-scan event or calibration data, so thatthe scanned line 1350 may be identified separately from other scannedlines, such as an adjacent line 1352. Adjacent line 1352 is associatedwith it its own region bounded by 1364 and 1366. Multiple scanned linesmay be projected simultaneously, where each scanned line is uniquelyidentified, even when projected onto a surface that is not substantiallyflat.

FIG. 14 illustrates an example of a pattern-projection system 1470. Thepattern-projection system 147 may be incorporated with, part of or acomponent of the electrical circuit 112. The pattern-projection system1470 includes a scanner mirror driver circuit 1472 and a laser drivercircuit 1474. The mirror driver circuit 1472 includes a RAM-basedarbitrary waveform generator (AWG) 1476, 1477 and a transconductancepower amplifier stage 1478, 1480 corresponding to a scanner 1482, 1483.

The AWG 1476 corresponding to a high speed scanner 1482 includes a16-entry waveform table 1484 and a 12-bit digital-to-analog converter(DAC) 1486. The waveform table 1484 may be incremented at approximately320 KHz to produce a sinusoidal waveform of approximately 20 KHz.

The AWG 1477 corresponding to a low-speed scanner 1483 includes a666-entry waveform table 1485 and a 12-bit DAC 1487. The waveform table1485 is incremented once per high-speed mirror cycle to produce asinusoidal waveform of approximately 30 Hz. The two AWGs 1476, 1477create a repeating raster pattern at approximately 30 frames per second.Electrical signals synchronize a camera system to the scanner driver. Areference input to each DAC 1486, 1487 is driven by a variable voltage1492, 1493 to dynamically adjust the horizontal and vertical dimensionsof the raster.

The high-speed scanner 1482 is driven at a resonance frequency in therange of about 20 KHz. A position feedback signal of the scanner 1482may be used with a closed-loop control using a DSP 1495 and a DDS 1496to adjust drive frequency of the drive signal to track variation in theresonance frequency. The frame rate of the raster pattern may changewith the high-speed resonance frequency of the scanner 1482. An exampleof the DSP includes model number TMS320LF2407A by Texas Instruments. Anexample of the DDS includes model number AD9834 by Analog Devices.

The laser driver circuit 1470 may include a multiple-bank random accessmemory (RAM)-based pattern table 1488 and a laser diode currentmodulator 1490. The RAM-based pattern table 1488 includes multiple banksof memory, where each bank includes a bit-mapped pixel image to bedisplayed during a single-pattern frame. A counter synchronized with theraster of the scanner raster generator accesses the pattern table 1488and to present the pixel data to the laser diode current modulator 1490to produce a repeating pattern. Each bank of the pattern table 1488 maybe loaded with a discrete pattern. Multiple single-pattern frames may becombined into repeating multiple-frame sequences with linked-listmechanism.

FIG. 15 illustrates a laser digitizer 1500 configured as an opticalcoherence tomography (“OCT”) or confocal sensor. The laser digitizerincludes a fiber-coupled laser 1511. The laser source 1511 may be a lowcoherence light source coupled to a fiber optic cable 1510, coupler 1509and detector 1501. The coupler, an optical delay line 1505 and reflector1504 return delayed light to the coupler 1509. The coupler 1509 splitsthe light from the light source into two paths. The first path leads tothe imaging optics 1506, which focuses the beam onto a scanner 1507,which steers the light to the surface of the object. The second path oflight from the light source 1511 via the coupler 1509 is coupled to theoptical delay line 1505 and to the reflector 1504. This second path oflight is of a controlled and known path length, as configured by theparameters of the optical delay line 1505. This second path of light isthe reference path. Light is reflected from the surface of the objectand returned via the scanner 1507 and combined by the coupler 1509 withthe reference path light from the optical delay line 1505. This combinedlight is coupled to an imaging system 1501 and imaging optics 1502 via afiber optic cable 1503. By utilizing a low coherence light source andvarying the reference path by a known variation, the laser digitizerprovides an Optical Coherence Tomography (OCT) sensor or a Low CoherenceReflectometry sensor. The focusing optics 1506 may be placed on apositioning device 1508 in order to alter the focusing position of thelaser beam and to operate as a confocal sensor.

Although embodiments of the invention are described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas described by the appended claims. The laser source may include alaser or LED, and the collimating optics may include optics thatcircularize the generally elliptical beam-produced by such sources. Thissystem may produce a circular spot on the object to provide a generallyuniform line when the beam scanned across the object.

The light source may positioned proximate to the intra-oral laserdigitizer remotely through a light guide such as optical fiber. Thelight source may be remote from the sensor structure and to provide foran intra-oral device having smaller dimensions.

A second light source (LED, incandescent bulb, laser, or other) mayprovide a background light so that the intra-oral laser digitizer may beused as a standard 2D dental camera. This second light source may belocated at or near the imaging optical path. The second light sourcealso may be placed remote to the sensor structure with the light broughtto the optical path through a light guide.

The intra-oral system also may include a one- or two-axis tilt sensor.The computer may monitor the angles of the tilt sensor, and the receivedimages of the scanned lines to determine a profile for the object. Aone-, two- or three-axis accelerometer may determine approximateposition changes of the intra-oral digitizer in one, two or three axes.

The system also may include a laser light source having a high speedmodulation system. The modulation system switches the laser on and offat a high rate (typically several MHz), reducing the coherence of thelaser source and degree of speckle produced by the laser source on theobject.

The scanning system may include a single mirror that scans in twoorthogonal axes or other non-parallel arrangement. An example of such amicro-mirror scanner is the bi-axial MEMS scanner of Microvision ofWashington. The scanning system may include two mirrors that scan in twoorthogonal directions or other non-parallel arrangement.

The imaging sensor may be CMOS sensor or a CCD sensor that capturesimages at high speeds. A processor processes captured images, such thatif the probe moves relative to the object, the software adjusts thecaptured data so that an accurate digitization occurs. The imagingsystem may include a small image sensor and objective lens mounteddirectly at the end of the sensor probe to provide a smaller intra-oralprobe through elimination of the relay lenses.

The laser source may include a laser source and line generating optics.This laser source produces one or more lines directed to a one axislaser scanner to provide for a low speed scanner or no scanner based onthe line generating optics producing sufficient number of separate linesegments.

The imaging system may include an objective, relay lens, asymmetric lenssystem, and a linear sensor array. A linear sensor array or analogposition sensor may be read for each pixel position. The asymmetric lensimages the scanning field onto the line detector. The triangulationangle causes the laser spot to be imaged onto different elements of theline detector as the object height changes, allowing fast scanning ofthe object.

A series of imaged laser segments on the object from a single sampleposition interlace between two or multiple 3D maps of the sample fromessentially the same sample position. The time period to measure eachinterlaced 3D map is reduced to a short interval and relative motioneffects between the intra-oral device and the patient are reduced. Theinterlaced 3D maps may be aligned with software to produce an effectivesingle view dense 3D point cloud that has no motion induced inaccuraciesor artifacts. For example, in a 10 step interlacing scheme, each imagemay be captured in 1/30^(th) of a second. When scanning over 0.3seconds, the present invention reduces affects of operator motion. Themotion of the operator between each subframe may be trackedmathematically through reference points in the dataset itself. Theoperator motion is removed in subsequent analysis, allowing a systemwith a framerate significantly lower than would otherwise be required.

Multiple dense 3D point clouds also may be acquired from approximatelythe same position, and mathematically aligned (i.e., moved relative toeach other to minimize the distance between them so as to cause relatedfeatures in each to become superimposed), and statistical methods usedto further improve the accuracy of the data (for example, Gaussianfiltering).

A low resolution pre-scan of the surface determines approximategeometry. Referring to this pre-scan, an approximate envelope ofsubsequent laser lines is determined by performing inverse calculationof a laser line centroid to 3D coordinate. Since these envelopes are notrectangular and combined with the assumption that the surface does notchange dramatically locally one can greatly increase the number ofsimultaneous lines projected on the surface and identifiable in theimage, increasing the effective scanning rate. In and example of N linesbeing scanned simultaneously with a system capable of processing Fframes per second, an effective F*N frames per second processing rate,or multiplied by a factor of N, may be achieved.

The imaging system may be located remotely from the imaging sensor.Through relay optics such as a coherent fiber imaging bundle, thescanning system may be located remotely from the imaging sensor. TheFourier transform of the object image is transferred through the fiberimaging bundle. By transferring the Fourier transform through the fiberbundle, more of the high frequency components of the object imageremain. Also, the effects of the fiber bundle can be removed by removingthe frequency components from the Fourier transformed image, whichcorresponds to the fiber bundle.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of theinvention. Accordingly, the invention is not to be restricted except inlight of the attached claims and their equivalents.

1. An intra-oral laser digitizer system comprising: a first light sourcehaving collimating optics configured to generate a collimated beam oflight; a scanner optically coupled to the first light source andconfigured to scan the collimated beam along at least two axes togenerate a pattern; an optics relay coupled to the scanner andconfigured to relay the pattern towards a remote object to be imaged; animage optics system having an optical axis configured to detect areflection of the pattern from the remote object at an angle θ withrespect to the optics relay and to generate data representative of asurface of the object based on the reflection of the pattern; aprocessor coupled to the scanner and the image optics system configuredto generate a three-dimensional image of the object based on the data;and a second light source located adjacent the optical axis to provide abackground light.
 2. The intra-oral laser digitizer of claim 1 where theremote object comprises any one of: an in vivo dental item, a dentalpreparation, a dental model, a dental mold, or a dental casting.
 3. Theintra-oral laser digitizer of claim 1 where the first light sourcecomprises a low coherence light source.
 4. The intra-oral laserdigitizer as described in claim 1 wherein the image optics systemcomprises an image sensor, an optical element that detects thereflection of the pattern, and an optics relay coupled to the opticalelement and configured to relay the reflection of the pattern from theoptical element to the image sensor.
 5. The intra-oral laser digitizeras described in claim 23 wherein the optics relay coupled to the opticalelement is co-linear to the optics relay coupled to the scanner.
 6. Anintra-oral laser digitizer, comprising: a first light source havingcollimating optics configured to generate a collimated beam of light; ascanner optically coupled to the light source and configured to scan thecollimated beam along at least two axes to generate a pattern comprisinga set of segments; a first optics relay coupled to the scanner andconfigured to relay the pattern towards a remote object to be imaged; anoptical element configured to detect a reflection of the pattern fromthe object at an angle θ with respect to the first optics relay; asecond optics relay, co-linear to the first optics relay, the secondoptics relay coupled to the optical element and configured to relay thereflection of the pattern toward an image sensor; and a second lightsource that provides a background light.
 7. The intra-oral laserdigitizer as described in claim 6 wherein the image sensor generates afirst data set representative of a surface of the object based on thereflection of the pattern.
 8. The intra-oral laser digitizer asdescribed in claim 7 wherein the scanner generates a second patterncomprising a set of segments, and wherein the image sensor generates asecond data set representative of a surface of the object based on areflection of the second pattern.
 9. The intra-oral laser digitizer asdescribed in claim 8 further including a processor, under programcontrol, to generate a three-dimensional image of the object based onthe first and second data sets.
 10. The intra-oral laser digitizer asdescribed in claim 9 further including a program-controlled processorthat generates a representation of the object based on the reflection ofthe pattern as detected by the image sensor.